INTRODUCTION

Until recently there was no comprehensive neuroanatomical atlas either in paper or electronic format on which to base studies of cetacean brain organization and function. We have published introductory paper atlases for three species,using magnetic resonance images (MRI) (Marino et al. 2001a, b, c), and we are here constructing an anatomically- labeled three-dimensional atlas, created from MRI images and stained sections of the brain of one of the most studied species of cetaceans, the bottle nose dolphin, Tursiops truncatus.

Differing techniques used to study the anatomy of the human brain all have their advantages and disadvantages. Magnetic resonance imaging (MRI) allows for the three-dimensional viewing of the brain and structures, precise spatial relationships and some differentiation between types of tissue, however, the image resolution is somewhat limited. Stained sections, on the other hand, offer excellent resolution and the ability to see individual nuclei (cell stain) or fiber tracts (myelin stain), however, there are often spatial distortions inherent in the staining process.

We here present an electronic anatomically labeled three-dimensional atlas of the dolphin brain created from MRI images. In conjunction we present anatomically labeled stained sections that correspond to the three-dimensional MRI images. In this way we utilize the advantages of both methods.

MATERIALS AND METHODS

MRI SpecimenThe MRI specimen is the postmortem brain of an adult pregnant female bottlenose dolphin (Tursiops truncatus) that stranded in February 1999 at Long Beach, North Carolina (Field# WAM 545). The carcass was in exceptionally fresh condition (Smithsonian Condition Code 2, Geraci and Loundsbury, 1993) with no evidence of damage. Total body length was 246 cm and total body weight was 238 kg. The brain, which was extracted from the skull approximately eight hours after the dolphin had died, was weighed and placed in 10% neutral buffered formalin, with the formalin being changed three times during the 39 days prior to scanning. Fresh brain weight was 1378 g. A small plug of cortical tissue was removed from the right cortical hemisphere of the fresh brain for biopsy purposes.

Three-Dimensional Reconstruction and ReformattingComputer-generated 3D reconstruction images were created using the software programs VoxelView and VoxelMath programs (Vital Images, Inc.) at the Laser Scanning Microscopy Laboratory at Michigan State University. The 3D rendered model, wherein details of internal and external morphology are represented in three-dimensional space, was then digitally resectioned in orthogonal planes to produce corresponding virtual section series in the horizontal (122 virtual sections) and sagittal (136 virtual sections) planes.

Anatomical Labeling and NomenclatureAll identifiable anatomical structures of the dolphin brain were labeled in the originally-acquired coronal plane images as well as in the images from the virtual sectioned brain in the sagittal and horizontal planes. The nomenclature used is from Morgane et al. (1980) and from Paxinos and Watson (1998). As a guide to the identification of structures, the MRI scans and the sections from the 3D reconstruction of the dolphin brain were compared with the published photographs and illustrations of the bottlenose dolphin brain from Morgane et al., 1980. All scans were also compared with a complete alternate series of sections stained, respectively, for cell bodies (Nissl method), and for myelinated fibers in the same three orthogonal planes (coronal or transverse, sagittal, and horizontal). These stained section series are from the Yakovlev-Haleem collection at the National Museum of Health and Medicine, Armed Forces Institute of Pathology.